This invention relates to radiation detectors, and is more in particular directed to the provision of a radiation detector, for example for X-rays or gamma-rays, wherein the detector is scanned with respect to a radiation source in order to develop signals for the production of an image.
Radiation imaging detector systems such as disclosed in U.S. Pat. No. 3,011,057, Anger, have found widespread use in nuclear medicine applications as a diagnostic tool to delineate one type of tissue, e.g., cancer cells, from another by the pattern of distribution of a radioactive compound introduced into the subject's body. As currently incorporated, these systems generally employ a massive high density collimator of the multi-hole, straight-bore or focusing type to distinguish between gamma-ray photons coming from one particular direction and those coming from other directions. While these systems lend themselves to the direct formation of an image, the use of the radiation-absorbing collimator severely limits the geometrical efficiency of these devices. Thus, in nuclear medicine applications, very large amounts of radioactivity must be present to overcome the count-rate restriction of the collimator and form an image of the radioactive deposition in a reasonable time. Generally, of course, the medical benefit obtained outweighs the possible harmful effects of the radiation to the subject.
Conversely, in the field of health physics, it is often necessary to make a measurement of small amounts of a given radioactivity isotope accidentally inhaled or otherwise ingested into the body, for purposes of assessing possible long-term dose effects. For more accurate body-burden estimations, as well as dose assessment, it is necessary to know the site of deposition in addition to measuring the amount of the activity. The instrument generally employed for measuring low levels of accidentally ingested radioactivity is the whole-body counter, a shielded enclosure in which large NaI(Tl) crystals and other types of radiation detectors are used to detect and measure the gamma-ray photons being emitted from the "whole body" of the subject. These detectors, as used, have very good geometric efficiency and are thus sensitive to small amounts of radiation; however, their spatial resolution is very poor. In this case, of course, collimators cannot be used to ascertain the site of deposition because of the small amounts of radioactivity present.
In view of the disadvantage of both above types of systems--i.e., the necessity of using large amounts of radioactivity with externally collimated nuclear medicine devices and, conversely, the poor spatial resolution of uncollimated, but sensitive, devices used in health physics application, the present invention is directed to the provision of a detection system which combines the high sensitivity of a whole-body counting crystal with the spatial resolution of the detector system of U.S. Pat. No. 3,011,057.
The present invention is therefore directed to the provision of a radiation detector that overcomes the above disadvantages of prior art radiation detectors, and that simultaneously provides both high spatial resolution and high detection deficiency.
Briefly stated, the present invention provides a radiation detector arrangement wherein the detecting faces of the detecting elements are arranged at an acute angle to the plane of radiation, i.e., the plane parallel to the direction of relative movement between the radiation detector and the radiation to be detected. The remaining portions of the detector elements are shielded from receiving radiation from the source, by, for example, adjacent detecting elements or layers of high Z materials. As a consequence, the individual detector elements are sensitive to their position with respect to the radiation source, without the necessity of employing collimators.
In a preferred embodiment of the invention, the individual detector elements are wedge-shaped, and are arranged in groups of four to define detectors having pyramidal recesses. In further embodiments of the invention, four detecting elements may be arranged in a back-to-back relationship, in the array, to form pyramidal detectors. Alternatively, a pair of elements may be arranged back-to-back to form detectors in an array, the detectors being wedge-shaped. Still further, single detecting elements may be provided having pyramidal or conical recesses.
The detecting elements may be of any conventional type such as scintillation crystals, associated with corresponding photocensors, or semi-conductor radiation detectors having suitable electrodes. The invention is not limited to the type of radiation detector employed.
The outputs of the individual radiation detector elements may be processed, for example with iterative procedures, in order to develop an image of the radiation source.